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Free carrier induced substrate Free carrier induced substrate heating of the epitaxially grown heating of the epitaxially grown GaMnAsGaMnAs

Institute of Physics AS CR, Prague

Vit Novak, Kamil Olejnik, Miroslav Cukr

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GaMnAsGaMnAs

• Problem: limited Mn solubility

growth at T=220°C growth at T=230°C

7%Mn, 50 nm 7%Mn, 50 nm

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Measuring the (low) temperatureMeasuring the (low) temperature

• thermocouple x poor coupling

• optical pyrometry x weak radiation

x substrate transparent

• Band-gap spectroscopy

Shanabrook et al. (1992), Johnson et al. (1993),

Thompson et al. (1997)

commercially by kSA (BandiT)

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Band-gap spectroscopyBand-gap spectroscopy

spectrometer

substrate heater

GaAs

160°C sufficient!

>~

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GrowthGrowth

• minimum change in Ts measured by Tc

constant heater power

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GrowthGrowth

• minimum change in Ts measured by Tc

• large change in Ts measured by BES !

constant heater power

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Absorption spectrumAbsorption spectrum

substrate

+ GaMnAs

band-gap region

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Absorption spectrumAbsorption spectrum

really change of Ts !

substrate

+ 40°C

+ GaMnAs

band-gap region

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Absorption spectrumAbsorption spectrum

really change of Ts !

substrate

+ 40°C

+ GaMnAs

band-gap region NIR

phononsfree carriers

substrate

+ GaMnAs

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Model I.Model I.

naively:

solution:

But ! • obscured parameters

• inconsistencies with experiment

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Radiation heat exchangeRadiation heat exchange

1 2

Qin-2

Qout-2Qout-1

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Radiation heat exchangeRadiation heat exchange

1 2

Qin-2

Qout-2Qout-1

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Radiation heat exchangeRadiation heat exchange

phononsinterband

• substrate/epilayer absorptance s()

abso

rpta

nce

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Radiation heat exchangeRadiation heat exchange

phononsinterband

free holes

abso

rpta

nce

• substrate/epilayer absorptance s()

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Radiation heat exchangeRadiation heat exchange

phononsinterband

free holesabso

rpta

nce

• substrate/epilayer absorptance s()

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Radiation heat exchangeRadiation heat exchange

phononsinterband

free holes

abso

rpta

nce

• substrate/epilayer absorptance s()

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Radiation heat exchangeRadiation heat exchange

phononsinterband

• radiation sources

free holes

~250°C

abso

rpta

nce,

rad

ianc

e

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Radiation heat exchangeRadiation heat exchange

phononsinterband

~900°C

• radiation sources

free holes

abso

rpta

nce

abso

rpta

nce,

rad

ianc

e

~250°C

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Radiation heat exchangeRadiation heat exchange

phononsinterband

• radiation sources

free holes

backgroundabso

rpta

nce,

rad

ianc

e

~250°C

~900°C

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Radiation heat exchangeRadiation heat exchange

phononsinterband

• substrate radiation

free holes

background

substrate

abso

rpta

nce,

rad

ianc

e

~250°C

~900°C

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Model II.Model II.

better:

heater ( 200°C )

cells ( ~ 900°C )

background ( > 77K, < 200°C )

i : >~

s(, t) :t

f

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ResultsResults

before growth: long after growth:

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ResultsResults

before growth: long after growth:

time evolution: Th = 320°C

Tc = 950°C

Tb = 40°C

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Implications for Implications for T T reductionreduction• TBES-locked substrate heater power

(problem: heat capacity of heater)

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Implications for Implications for T T reductionreduction• TBES-locked substrate heater power

(problem: heat capacity of heater)

• sample holder (or sample!) with initially strong IR absorption

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Implications for Implications for T T reductionreduction• TBES-locked substrate heater power

(problem: heat capacity of heater)

• sample holder (or sample!) with initially strong IR absorption

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Implications for Implications for T T reductionreduction• TBES-locked substrate heater power

(problem: heat capacity of heater)

• sample holder (or sample!) with initially strong IR absorption

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Implications for Implications for T T reductionreduction• TBES-locked substrate heater power

(problem: heat capacity of heater)

on Mo-block

w/ sublayer

• sample holder (or sample!) with initially strong IR absorption

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Bonus: record Curie temperatureBonus: record Curie temperature

185K

also: Nottingham group

Thank you !Thank you !